The present invention relates to a glass shaping mold for imparting a desired shape to a heat-softened glass sheet or gob.
Heat-softened glass sheets or gobs have conventionally been shaped by glass shaping molds. When bending a heat-softened glass sheet in direct contact with the shaping surfaces of shaping molds, the glass sheet tends to stick partially to the shaping surfaces or be locally cooled by the shaping surfaces, resulting in the likelihood of producing certain optical defects in the glass sheet.
One solution has been to apply a cover of flexible fiber glass cloth against the shaping surface of a bending mold for preventing the glass sheet from sticking to the shaping surface and providing heat insulation between the shaping surface and the glass sheet, as disclosed in U.S. Pat. No. 4,274,857 to Wolfe. However, the fiber glass cloth cover is liable to leave cloth marks on the surface of the bent glass sheet. The bent glass sheet therefore has small surface irregularities which are responsible for optical defects such as light transmitting and reflecting distortions. The glass surface irregularities could be reduced by employing thinner glass fibers for the fiber glass cloth cover. The fiber glass cloth cover would however become less durable and might be broken in use. If the fiber glass cloth cover were broken, the glass surface would have large irregularities and the fiber glass cloth cover would be unraveled progressively from the broken region.
It would be difficult to increase the thickness of the fiber glass cloth cover. Where the fiber glass cloth cover is applied to the bending mold surface, the cloth cover is gradually burned away and reduced in thickness in use. Consequently, the fiber glass cloth cover is required to be replaced at frequent intervals.